I tried to utilize the web to figure the optimum size ratio for an ancient Roman torsion spring, (e.g. it’s length vs. it’s diameter). The varying opinions quickly got me disoriented. It was all a bit of a muddle.

So I’ve decided to use a “cut the chatter” kind of strategy and act from what I know already. Because Firefly’s springs have proven themselves highly successful over the years, especially with the short limb rotations we are currently exploring, I will use that same spring ratio on Phoenix. That is: 6.6 times as long as they are wide in diameter. 6.6 to 1, if you will.

Firefly has not had her springs adjusted in the last 4 years and has always shot a very consistent 316 fps, plus or minus 10 fps. Her power is enough to shoot a 520 gram bolt 800 yards. I believe that if there are gains to be made in performance they will be found somewhere other than the spring ratio. “The spring ratio is not to be monkeyed with!”, says my executive function. A voice that demands obedience from the other functions that keep this project puttering along.

Developing Firefly’s torsion springs was not an easy process. When gains are hard-won, one tends to be less flippant in considering potential “improvements”. Counting one’s blessings can make a lot of sense.

Here is a preview of one of Phoenix’s washers, shown in cross section.

The new washers will be 2 3/4″ inches long. This will make Phoenix’s springs about 16 1/2 ” long, and with their 2 1/2″ diameter, they will be 6.6 times longer than they are wide.

And so, in a gesture of mathematically precise conservatism, Phoenix’s spring ratio will be exactly the same as her older sibling, because, well … why not? That’s how pleased I am with the performance generated by Firefly’s spring ratio. No changes needed for Phoenix in this area.

Many thanks to long time contributor to this blog, Mr. Charles Fink, for sending us some handsome billets of Bois d’arc timber from Texas.

The unique properties of this wood (also known as osage orange) will make some exceptionally strong ballista limbs. They have been cut recently and Charles waxed their ends to help prevent checking as they dry out. I have stored them in a cool area of the shop so that they have every chance of seasoning properly over the next year or so.

The authenticity police will no doubt censor us for using a New World wood on one of our Old World mechanisms, but, given the relative difficulty of obtaining high end timber these days, I am not overly concerned with their typically manic ravings. The Romans must have had an enormous selection of premium timber from the ancient forests of their far flung empire. We moderns are at a natural disadvantage when it comes to being choosy about the wood we utilize in these reconstructions. Allowances must be made.

That being said, Phoenix’s first set of limbs will be made from white ash, just like Firefly’s. All very authentic and tickety-boo.

It is important to let the new billets from Texas dry out slowly and completely before fashioning them into limbs. Thanks again Charles! They are some truly beautiful pieces of wood. Just the right size for Phoenix and unbelievably straight grained for this species.

Mr. John Payne is currently the tip of the spear with his wedge machine efforts on Vlad. (That’s, Vlad the Impaler, of course. Cool name for a remote skewering device, huh?)

Some serious iron frame wedgies going on here. Make those strands work for a livin’.

This is capital work! Nice and straight on the springs too. Just like Mr. Philon ordered.

I am hoping John will be able to make a first thrust at this whole question of “balance of power transfer”. Wedge balancing a ballista is the game. Doing it in a way that generates lots of power to boot, is the trick we must master.

Meanwhile I am setting up to cut out Phoenix’s washers and vernier plates. Chips can fly in earnest next week.

I am very grateful to him for taking the time to write this and post it on his website. It is invigorating to find another researcher who can play back your own intentions to you. They sound less half-baked when someone else shows that they understand what you are trying to accomplish.

Samuli has a more comprehensive knowledge of the artifacts than I do. The exceptions and alternate explanations he suggests are well founded. It is good to cultivate these reasonable reservations. They help to sharpen our focus and keep untoward claims in check. This is just an experiment after all. Like a signpost in the fog, it’s usefulness must depend on knowing what it does not point to, as much as what it does.

Now that the teak oil has had it’s way with the finish, Phoenix is more comfortable revealing her sensitive beak to the world.

I expect there are many who would say that the profile of the wood case on an ancient iron frame ballista should more nearly resemble a plank than some kind of swanky bird.

But the rectilinearists can keep their ubiquitous straight lines. All that right angled correctness makes me yawn. I’ll make-do with a smaller piece of the imaginary pie. The curvy bit, please! With a cherry on top!

Look, I get what a pain it must be to try and read this blog and figure out what exactly this experiment is that I keep beating on about. In the next few paragraphs I will try to abbreviate the process into as few a words as possible in the hope it may act as a signpost amid this terrifying clutter of verbiage.

Given that square crossbars, even those with a small corner radius, are quite damaging to the spring cord in high-power machines, why are there original crossbars that have a square cross section?

Answer: either the ancient machines were very low powered (not at all likely), or the Romans loved replacing their ballista springs every couple of hundred shots, or ……… wait for it ……… the square crossbars were likely part of some kind of wedge machine because wedge machines require square crossbars for their wedges to push against. (If you understand the mechanics of a wedge machine, this latter is self evident.)

The experiment with Phoenix will determine if it is possible to create high-power (say 1200 foot lbs or more, 350+ fps) and good balance with a wedge type system similar to the one described by Philon.

If the attempt is successful, it will not only suggest a reason why there were square crossbars, but also show it is possible to balance a torsion engine with a technique completely independent of washer rotation. This is important because it will provide a rationale for the unaccountably low number of washer locking holes on certain artifacts (e.g. the Lyon machine).